MCQ
The circle x2 + y2 + 2gx + 2fy + c = 0 does not intersect x-axis, if:
  • A
    g2 < c
  • B
    g2 > c
  • C
    g2 > 2c
  • D
    None of these

Answer

  1. g2 < c

Solution:

Given:

x2 + y2 + 2gx + 2fy + c = 0 ......... (1)

The given circle intersects the x-axis.

The equation of circle becomes x2 + 2gx + c = 0 ......... (2)

Solving equation (2):

$\therefore$ Discriminant, $\text{D}=\sqrt{4\text{g}^2-4\text{c}}\geq0$

$\Rightarrow4\text{g}^2-4\text{c}\geq0$

$\Rightarrow\text{g}^2-\text{c}\geq0$

$\Rightarrow\text{g}^2\geq\text{c}$

Hence, if g2 < c, then the given circle will not intersect the x-axis.

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